1. Field of the Invention
This invention relates in general to a polarization diplexer.
2. Description of the Prior Art
Microwave antennas which have band widths of 2:1 and more can be obtained using correspondingly broadband polarization diplexers for operation with two different polarizations. Such a polarization diplexer allows the combination with two frequency diplexers to form a polarization frequency diplexer which has been identified as a system diplexer that allows two radio link systems of adjacent frequency bands each having two linear polarizations to be switched into one and the same antenna. As compared to previous one band antennas, such two band antenna system has expanded transmission capacities for two radio links which is an advantage where limited space requirements occur on the radio tower.
Also, in satellite communication systems, transmission capacity can be increased by expanding the frequency ranges to extend above one octave, for example, 3.7 through 6.435 GHz up to the present time to 3.4 through 7.125 GHz in the future. Polarization diplexers which comprise useable frequency ranges of more than 2:1 and which avoid expensive ridge waveguides are not known in the prior art. Polarization diplexers such as described in U.S. Pat. No. 4,293,829 which comprise two E-plane offset sections and two H-plane offset sections as well as the polarization diplexer described in German OS No. 30 10 360 which comprise four E-H-plane offset sections also have a theoretical unambiguous frequency range of only 2:1; and this corresponds to a maximum useable frequency range of 1.73:1. The physical reasons for the fact that the unambiguous frequency range of such prior art polarization diplexers is limited towards higher frequencies is because in the H-plane bends they excite the TE.sub.20 spurious mode starting with the operating frequency at which the TE.sub.20 cutoff frequency is reached in the rectangular waveguide of the H-plane bend. As a consequence that .lambda..sub.cTE20 =a, the TE.sub.20 cutoff frequency of a H-plane bend only depends on the broadside dimensions a of the waveguide; and f.sub.cTE20 as well as the unambiguous frequency range f.sub.cTE20 /f.sub.cTE10 remain unchanged as compared to the normal profile waveguide with a=2b wherein the height b of the waveguide is reduced and a is retained constant. Also, both of H-plane bends as well as the H-plane corners exhibit the same behaviour.